This invention relates to start control arrangements for reversible alternating current split phase induction motors. More specifically, this invention relates to start control arrangements for selectively initiating rotation of the motor in one direction or the other.
Reversible motors of the split phase induction type are frequently used to drive domestic major appliances such as clothes washers, for example. Typically, the motor is selectively energized for rotation in one direction for wash and the other direction for spin.
Such motors include a start winding and a run winding connected in parallel and energized by a single phase power supply. The start winding is used to provide a rotating stator field to initiate rotation of the rotor. Once the motor gets up to or substantially up to speed, the start winding is deenergized to reduce power loss in the winding. In arrangements known in the art, the polarity of the start winding determines the direction of rotation of the motor. The direction of rotation can thus be reversed by reversing the polarity of the start winding relative to the run winding prior to energizing the winding. Typically, mechanical, electromechanical or electronic switch means are employed in series with the start winding to effectively reverse the connection linking the run winding to the power supply. This approach works satisfactorily; however, the polarity reversing means employed, such as electromechanical relay means or electronic switch means, add significant cost to the control system. Switch means, known in the art for deenergizing the start winding once the motor gets up to speed, include centrifugal switch means responsive to rotating motor speed, and operative to switch the winding out of the circuit when the motor attains a predetermined speed, and current actuated switch means responsive to the magnitude of the run current operative to open the start winding circuit when the run current drops below a predetermined threshold level. This approach also works satisfactorily; however, as in the case of conventional polarity reversal arrangements the conventional switch means employed for deenergizing the start winding adds cost to the control system.
A control arrangement for a reversible split phase induction motor which selectively initiates rotation of the motor in the desired direction without need for a relatively costly mechanical switch means for changing the polarity of the start winding and deenergizing the start winding when the motor gets up to speed is highly desirable.
It is therefore an object of the present invention to provide a control arrangement for a reversible split phase induction motor which selectively initiates rotation of the motor in the desired direction by phase controlling the start winding thereby eliminating the need for polarity reversing switch means.
It is a further object of the present invention to provide a control arrangement of the aforementioned type which monitors motor speed and inhibits triggering of the phase control means thereby deenergizing the motor start winding once the motor speed exceeds a predetermined threshold.